A preparation method and application of aramid insulation paper

Abstract

The invention discloses a preparation method and application of aramid insulating paper. Aramid precipitated fibrils are pulped and de-pulped, and a CTI additive containing a metal element is added thereto, followed by wet molding to prepare the aramid insulating paper. The CTI additive containing the metal element is wet-ground, a weak acid is added thereto to adjust the pH to 3-4, and then an alkali solution is used to adjust the pH to neutral. The aramid insulating paper prepared using the treated CTI additive can significantly improve its breakdown strength and leakage tracking index, prevent failure due to breakdown and surface electro-etching, and ensure its application as an insulating material in new energy vehicle motors.

Description

Technical Field

[0001] The present invention belongs to the technical field of papermaking and insulating materials, and in particular relates to a preparation method of aramid insulating paper and application thereof. Background Art

[0002] Aramid insulation paper used in new energy vehicle motors has high requirements for both mechanical and electrical strength. Aramid composite materials made from current aramid paper have low mechanical strength and are prone to bending and cracking during use. Furthermore, due to their low Comparative Tracking Index (CTI), they are susceptible to electrical corrosion, which affects their use.

[0003] Chinese patent document 202210542302.6 discloses a high-partial discharge insulation material for oil-cooled motors in new energy vehicles and its preparation method. The high-partial discharge insulation material includes a high-density aramid fiber layer, a first adhesive layer, a mica aramid fiber layer, a second adhesive layer, and a low-density aramid fiber layer arranged in sequence from top to bottom; wherein the first adhesive layer and the second adhesive layer are both acrylic modified polyurethane glue. Chinese patent document 202211246374.2 discloses an aramid insulating paper-based material for motor slot insulation and its preparation method. By adding shaped meta-aramid chopped fibers and optimizing the spinning process, the mechanical strength of the fibers is improved. The shaped chopped fibers increase the specific surface area of ​​the fibers, enhance the interfacial bonding strength between the meta-aramid chopped fibers and the meta-aramid precipitated fibers, and improve the tear strength of the paper. High thermal conductivity fillers are added to optimize the thermal conductivity of the material.

[0004] The aramid materials or aramid insulation papers prepared in the above patent documents have insufficient improvement in mechanical properties such as tensile strength and bending resistance, and their resistance to leakage tracking is insufficient. Summary of the Invention

[0005] In order to overcome the technical problem of low CTI value of aramid insulation paper in the prior art, the present invention provides a preparation method and application of aramid insulation paper. The prepared aramid insulation paper greatly improves the breakdown strength and leakage tracking index of the aramid insulation paper, prevents failure due to breakdown and surface electro-etching, and ensures its application as an insulation material in new energy vehicle motors.

[0006] In order to solve the above technical problems, the technical solutions proposed by the present invention are as follows:

[0007] The present invention provides a method for preparing aramid insulating paper, comprising the following steps:

[0008] S1. By synergistically controlling the specific surface area, beating degree and fiber length of the aramid fibrids during the pulping and decomposition process, the aramid fibrids after pulping and decomposition are uniformly mixed with aramid chopped fibers to obtain an aramid fiber slurry;

[0009] S2, wet-grinding the CTI additive containing the metal element, then adding a weak acid to adjust the pH and letting it stand, and finally adjusting the pH to neutral with an alkaline solution to obtain the treated CTI additive;

[0010] S3, uniformly mixing the aramid fiber slurry obtained in step S1 and the treated CTI additive obtained in step S2, and wet-forming the mixture, followed by pressing, drying, curling, and high-temperature rolling to obtain aramid insulating paper.

[0011] In the present invention, aramid fibrids are pulped and debonded to obtain a large specific surface area and free of excessively long fibers. The treated aramid fibrids are then mixed with aramid short fibers. The aramid short fibers are equivalent to "rebar in reinforced concrete" in aramid paper, providing mechanical strength and structural support for the aramid paper. The aramid short fibers and the treated aramid fibrids are combined in proportion to obtain optimal comprehensive performance. The CTI additive is wet-ground to control the particle size of the CTI additive within a certain range. The ground CTI additive is then adjusted to a pH of 3 to 4 with a weak acid and allowed to stand. The surface of the CTI additive is micro-treated with a weak acid to promote the hydrolysis of metal ions on its surface to form hydroxyl groups, thereby increasing the surface activity of the CTI additive. The surface-activated CTI additive is then adjusted to a neutral pH with a sodium hydroxide solution. The surface-activated CTI additive is more likely to form a positively charged colloid at this pH, which can better combine with the negatively charged aramid fiber, thereby increasing the retention rate of the CTI additive. The CTI additive destroys the local carbon loop caused by electro-etching through nucleation and other means, thereby preventing further electro-etching effects. The CTI additive of the present invention is mixed with the aramid fiber before papermaking and is formed into paper together. It exists inside the aramid insulating paper and improves the tracking resistance by blocking the formation of the carbon loop. This is different from the method of providing a silica or alumina coating on the surface coating of the aramid insulating paper to improve the breakdown voltage and corona resistance. By controlling the specific surface area, beating degree and fiber length by the pulping and deflaking machine, the mechanical strength of the product of the present invention can be better synergistically improved.

[0012] As an optional embodiment, in the preparation method provided by the present invention, in step S2, the CTI additive consists of silicon dioxide and metal oxide / metal hydroxide.

[0013] In the present invention, the composite addition of silicon dioxide and metal oxides / hydroxides is selected by comprehensively considering factors such as raw material cost, toxicity, color, stability of oxides / hydroxides, and moisture absorption.

[0014] As an optional embodiment, in the preparation method provided by the present invention, in step S2, the molar ratio of silicon dioxide to metal oxide / metal hydroxide in the CTI additive is 1:5 to 1:20.

[0015] In the present invention, the molar ratio of silica to metal oxide / metal hydroxide in the CTI additive is set at 1:5 to 1:20. If the silica content is too high, it may be encapsulated in the colloidal particles, reducing the stability of the colloidal particles. If the silica content is too low, the colloidal stabilization effect is not significant, resulting in poor results. Adding an appropriate amount of silica can further improve the stability of the colloidal particles.

[0016] As an optional embodiment, in the preparation method provided by the present invention, the metal oxide / metal hydroxide is selected from one of magnesium, aluminum, and zinc.

[0017] The oxides / hydroxides of magnesium, aluminum and zinc are selected in the present invention for the purpose of low cost, no introduction of other colors, non-toxicity, good stability and no moisture absorption, and are therefore better additives.

[0018] As an optional embodiment, in the preparation method provided by the present invention, the metal oxide / metal hydroxide is selected from one of magnesium hydroxide, aluminum hydroxide, zinc hydroxide, aluminum oxide, magnesium oxide or zinc oxide.

[0019] As an optional embodiment, in the preparation method provided by the present invention, in step S2, a weak acid is added to adjust the pH to 3-4.

[0020] As an optional embodiment, in the preparation method provided by the present invention, the added mass of the CTI additive is 3-7% of the total dry mass of the aramid fibrid and the aramid chopped fibers.

[0021] The amount of the additive in the present invention is controlled within 3-7% of the total dry mass of the fiber. If the amount of the additive is too little, the improvement effect will be ineffective; if the amount of the additive is too high, slag may fall off, and even affect the structure of the aramid paper.

[0022] As an optional embodiment, in the preparation method provided by the present invention, in step S2, the particle size D90 of the CTI additive after grinding is 5 to 50 microns.

[0023] In the present invention, the particle size D90 of the additive is 5 to 50 microns. If the particle size is too small, the preparation process will be complicated and time-consuming; if the particle size is too large, the retention rate of the additive in the aramid insulation paper will be affected, and even slag will fall off.

[0024] Preferably, in step S2, the particle size D90 of the CTI additive after grinding is 10 to 30 microns.

[0025] As an optional embodiment, in the preparation method provided by the present invention, the weak acid is selected from one of citric acid and acetic acid.

[0026] Using weak acid to adjust the pH of the solution can control the reaction rate and prevent strong acid from dissolving metal oxides / metal hydroxides.

[0027] As an optional embodiment, in the preparation method provided by the present invention, in step S2, the concentration of the weak acid is 0.05 to 0.15 mol / L.

[0028] The weak acid concentration should be controlled within this range to avoid excessive dissolution of metal oxides / metal hydroxides. Too high a concentration will cause the particles to dissolve, while too low a concentration will result in a slow reaction and poor effect.

[0029] As an optional embodiment, in the preparation method provided by the present invention, in step S2, a weak acid is added to adjust the pH to 3-4 and then the mixture is allowed to stand for 20-40 minutes.

[0030] In the present invention, the standing time is controlled within 20 to 40 minutes. If the treatment time is too short, the metal ions will not be fully hydrolyzed, and if the treatment time is too long, the particles will settle.

[0031] As an optional embodiment, in the preparation method provided by the present invention, in step S2, the alkali solution is selected from one of a strong base or a weak base, the strong base is sodium hydroxide, and the weak base is aqueous ammonia.

[0032] When alkaline solution is used to adjust the pH in the present invention, the sodium hydroxide used is at a low concentration. The sodium hydroxide solution is carefully added dropwise to the acidic aqueous solution system to preferentially react with hydrogen ions. Although aluminum oxide and zinc oxide are amphoteric, their reaction process with sodium hydroxide is to some extent subject to kinetic limitations.

[0033] As an optional embodiment, in the preparation method provided by the present invention, the CTI additive is composed of silica and alumina, the molar ratio of silica to alumina is 1:10-15, and the particle size D90 of the CTI additive after grinding is 10-30 μm.

[0034] As an optional embodiment, in the preparation method provided by the present invention, in step S1, the specific surface area of ​​the aramid fibrils after pulping and decomposition treatment is 70 to 120 m 2 / g, beating degree is 60-85°SR, and fiber length is ≤2mm. By controlling the specific surface area, beating degree and fiber length by the pulping and deflaking machine, the mechanical strength of the product of the present invention can be better synergistically improved.

[0035] As an optional embodiment, in the preparation method provided by the present invention, in step S3, the drying temperature is 40-105°C, the pressure of the high-temperature roller pressing is 150-350 N / m, and the temperature is 220-340°C.

[0036] As an optional embodiment, in the preparation method provided by the present invention, in step S2, the CTI of the aramid insulation paper is ≥325V.

[0037] As an optional embodiment, in the preparation method provided by the present invention, the aramid fibrid is meta- or para-aramid fibrid.

[0038] As an optional embodiment, in the preparation method provided by the present invention, the aramid short fibers are meta- or para-aramid short fibers.

[0039] Based on the same technical concept, the present invention also provides the use of aramid insulation paper prepared by the above-mentioned preparation method of aramid insulation paper in new energy vehicle motors.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) In the present invention, the aramid fibrils are pulped and decomposed, and the CTI additive containing metal elements is treated and then added to the treated aramid fibrils. The prepared aramid insulating paper can greatly improve its breakdown strength and leakage tracking index, prevent failure due to breakdown and surface electro-etching, and ensure its application as an insulating material in new energy vehicle motors.

[0042] (2) The method for preparing aramid insulation paper of the present invention does not use any chemical additives, thereby reducing pollution to the environment and promoting the green manufacturing of aramid insulation paper. DETAILED DESCRIPTION

[0043] To facilitate understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0044] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0045] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0046] 1. Preparation of aramid insulation paper for new energy vehicle motors

[0047] Example 1

[0048] A method for preparing aramid insulation paper for new energy vehicle motors comprises the following steps:

[0049] (1) The aramid fibrid was processed by pulping machine and debonding machine, and the specific surface area of ​​the obtained aramid fibrid was 95m 2 / g, a beating degree of 72°SR, a slurry concentration of 0.12%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0050] (2) CTI additives are magnesium hydroxide and silicon dioxide, with a molar ratio of 10:1 and an addition ratio of 4% of the total dry mass of the fiber. Ultrasonic wet grinding is performed in water to a particle size D90 of 10 μm. Then, 0.05 mol / L citric acid is carefully added to the additive, and the pH of the solution is adjusted to 3-4. The solution is allowed to stand for 30 minutes, and the pH of the solution is carefully adjusted to neutral with sodium hydroxide solution to form a positively charged colloid.

[0051] (3) 55 parts by weight of the treated aramid fiber slurry, 45 parts by weight of aramid short-cut fibers and the treated CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.06% and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0052] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0053] (5) The aramid insulation base paper is hot-pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 270 N / m and a hot-pressing temperature of 300°C to produce 2 mil aramid insulation paper for new energy vehicle drive motors.

[0054] Example 2

[0055] A method for preparing aramid insulation paper for new energy vehicle motors comprises the following steps:

[0056] (1) The aramid fibrils were processed by pulping machine and deflaking machine, and the obtained aramid fibrils had a specific surface area of ​​80m 2 / g, a beating degree of 68°SR, a slurry concentration of 0.15%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0057] (2) The CTI additives are aluminum oxide and silicon dioxide, with a molar ratio of 15:1 and an addition ratio of 6% of the total dry mass of the fiber. Ultrasonic wet grinding is performed in water to a particle size D90 of 30 μm. Then, 0.15 mol / L acetic acid is carefully added to the additive, and the pH of the solution is adjusted to 3-4. The solution is allowed to stand for 40 minutes, and the pH of the solution is carefully adjusted to neutral with sodium hydroxide solution to form a positively charged colloid.

[0058] (3) 60 parts by weight of the treated aramid fiber slurry, 40 parts by weight of aramid short fibers and the treated CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.24% and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0059] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0060] (5) The aramid insulation base paper is hot pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 290 N / m and a hot pressing temperature of 295°C to produce 2 mil aramid insulation paper for new energy vehicle drive motors.

[0061] Example 3

[0062] A method for preparing aramid insulation paper for new energy vehicle motors comprises the following steps:

[0063] (1) The aramid fibrils were processed by pulping machine and deflaking machine, and the obtained aramid fibrils had a specific surface area of ​​90m 2 / g, a beating degree of 78°SR, a slurry concentration of 0.14%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0064] (2) The CTI additives are zinc oxide and silicon dioxide, with a molar ratio of 12.5:1. The addition ratio is 3.5% of the total dry mass of the fiber. Ultrasonic wet grinding is carried out in water to a particle size D90 of 25 μm. Then, 0.1 mol / L citric acid is carefully added to the additive, and the pH of the solution is adjusted to 3-4. The solution is allowed to stand for 30 minutes, and the pH of the solution is carefully adjusted to neutral with sodium hydroxide solution to form a positively charged colloid.

[0065] (3) 57 parts by weight of the treated aramid fiber slurry, 43 parts by weight of aramid short-cut fibers and the treated CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.21%, and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0066] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0067] (5) The aramid insulation base paper is hot-pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 280 N / m and a hot-pressing temperature of 295°C to produce 2 mil aramid insulation paper for new energy vehicle drive motors.

[0068] Example 4

[0069] A method for preparing aramid insulation paper for new energy vehicle motors comprises the following steps:

[0070] (1) The aramid fibrils were processed by pulping machine and deflaking machine, and the obtained aramid fibrils had a specific surface area of ​​90m 2 / g, a beating degree of 78°SR, a slurry concentration of 0.14%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0071] (2) Aluminum hydroxide was used as a CTI additive at a ratio of 10% of the fiber's absolute dry mass. Ultrasonic wet grinding was performed in water to a particle size D90 of 25 μm. Acetic acid at a concentration of 0.01 mol / L was then carefully added dropwise to the additive to adjust the solution pH to 3-4. The solution was allowed to stand for 30 minutes, and then the pH of the solution was carefully adjusted to neutral using sodium hydroxide solution.

[0072] (3) 57 parts by weight of treated aramid fiber slurry, 43 parts by weight of aramid short-cut fibers and ground CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.21%, and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0073] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0074] (5) The aramid insulation base paper is hot-pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 280 N / m and a hot-pressing temperature of 295°C to produce 2 mil aramid insulation paper for new energy vehicle drive motors.

[0075] Example 5

[0076] A method for preparing aramid insulation paper for new energy vehicle motors comprises the following steps:

[0077] (1) The aramid fibrils were processed by pulping machine and deflaking machine, and the obtained aramid fibrils had a specific surface area of ​​90m 2 / g, a beating degree of 78°SR, a slurry concentration of 0.14%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0078] (2) The CTI additives are ferric oxide and silicon dioxide, with a molar ratio of 7:1 and an addition ratio of 3.8% of the total dry mass of the fiber. Ultrasonic wet grinding is performed in water to a particle size D90 of 25 μm. Then, 0.1 mol / L citric acid is carefully added to the additive, and the pH of the solution is adjusted to 3-4. The solution is allowed to stand for 30 minutes, and the pH of the solution is carefully adjusted with sodium hydroxide solution to form a positively charged colloid.

[0079] (3) 57 parts by weight of the treated aramid fiber slurry, 43 parts by weight of aramid short-cut fibers and the treated CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.21%, and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0080] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0081] (5) The aramid insulation base paper is hot-pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 280 N / m and a hot-pressing temperature of 295°C to produce a 2 mil aramid insulation paper for new energy vehicle drive motors with a distinct yellow color.

[0082] Example 6

[0083] A method for preparing aramid insulation paper for new energy vehicle motors comprises the following steps:

[0084] (1) The aramid fibrils were processed by pulping machine and deflaking machine, and the obtained aramid fibrils had a specific surface area of ​​90m 2 / g, a beating degree of 78°SR, a slurry concentration of 0.14%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0085] (2) The CTI additives are zinc oxide and silicon dioxide, with a molar ratio of 4:1 and an addition ratio of 3.5% of the total dry mass of the fiber. Ultrasonic wet grinding is performed in water to a particle size D90 of 25 μm. Then, 0.1 mol / L citric acid is carefully added to the additives, and the pH of the solution is adjusted to 3-4. The solution is allowed to stand for 30 minutes, and the pH of the solution is carefully adjusted to neutral with sodium hydroxide solution to form a positively charged colloid.

[0086] (3) 57 parts by weight of the treated aramid fiber slurry, 43 parts by weight of aramid short-cut fibers and the treated CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.21%, and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0087] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0088] (5) The aramid insulation base paper is hot-pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 280 N / m and a hot-pressing temperature of 295°C to produce 2 mil aramid insulation paper for new energy vehicle drive motors.

[0089] Comparative Example 1 (no CTI additive added):

[0090] A method for preparing aramid insulating paper comprises the following steps:

[0091] (1) The aramid fibrid was processed by pulping machine and debonding machine, and the specific surface area of ​​the obtained aramid fibrid was 95m 2 / g, a beating degree of 72°SR, a slurry concentration of 0.12%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0092] (2) 55 parts by weight of the treated aramid fiber slurry and 45 parts by weight of aramid short-cut fibers were transported from a hydraulic headbox to a fourdrinier paper machine for wet forming. The forming concentration was 0.06%, and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0093] (3) The formed paper is pressed and dried to obtain aramid insulation paper base paper.

[0094] (4) The aramid insulation base paper is hot pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 270 N / m and a hot pressing temperature of 300°C to produce 2 mil aramid insulation paper.

[0095] Comparative Example 2 (CTI additive only uses silicon dioxide):

[0096] A method for preparing aramid insulating paper comprises the following steps:

[0097] (1) The aramid fibrils were processed by pulping machine and deflaking machine, and the obtained aramid fibrils had a specific surface area of ​​90m 2 / g, a beating degree of 78°SR, a slurry concentration of 0.14%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0098] (2) Silica was used as a CTI additive at a ratio of 10% of the fiber's absolute dry mass. Ultrasonic wet grinding was performed in water to a particle size D90 of 25 μm. Acetic acid at a concentration of 0.01 mol / L was then carefully added dropwise to the additive to adjust the solution pH to 3-4. The solution was allowed to stand for 30 minutes, and then the pH of the solution was carefully adjusted to neutral with sodium hydroxide solution.

[0099] (3) 57 parts by weight of treated aramid fiber slurry, 43 parts by weight of aramid short-cut fibers and ground CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.21%, and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0100] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0101] (5) The aramid insulation base paper is hot pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 280 N / m and a hot pressing temperature of 295°C to produce 2 mil aramid insulation paper.

[0102] Comparative Example 3 (grinding only, without acid-base adjustment treatment):

[0103] A method for preparing aramid insulating paper comprises the following steps:

[0104] (1) The aramid fibrils were processed by pulping machine and deflaking machine, and the obtained aramid fibrils had a specific surface area of ​​90m 2 / g, a beating degree of 78°SR, a slurry concentration of 0.14%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0105] (2) The CTI additives are zinc oxide and silicon dioxide, with a molar ratio of 12.5:1 and an addition ratio of 10% of the total dry mass of the fiber. Ultrasonic wet grinding is performed in water to a particle size D90 of 25 μm.

[0106] (3) 57 parts by weight of treated aramid fiber slurry, 43 parts by weight of aramid short-cut fibers and ground CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.21%, and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0107] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0108] (5) The aramid insulation base paper is hot pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 280 N / m and a hot pressing temperature of 295°C to produce 2 mil aramid insulation paper.

[0109] Comparative Example 4 (grinding only, acid treatment only, no alkali treatment):

[0110] A method for preparing aramid insulating paper comprises the following steps:

[0111] (1) The aramid fibrils were processed by pulping machine and deflaking machine, and the obtained aramid fibrils had a specific surface area of ​​90m 2 / g, a beating degree of 78°SR, a slurry concentration of 0.14%, and an aramid fiber slurry with a fiber length of less than 2nm.

[0112] (2) The CTI additives used were zinc oxide and silicon dioxide, with a molar ratio of 12.5:1. The addition ratio was 3.5% of the total dry mass of the fiber. Ultrasonic wet grinding was performed in water to a particle size D90 of 25 μm. Then, 0.1 mol / L citric acid was carefully added dropwise to the additives, and the solution pH was adjusted to 3-4. The solution was allowed to stand for 30 min.

[0113] (3) 57 parts by weight of the treated aramid fiber slurry, 43 parts by weight of aramid short-cut fibers and the treated CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.21%, and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0114] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0115] (5) The aramid insulation base paper is hot pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 280 N / m and a hot pressing temperature of 295°C to produce 2 mil aramid insulation paper.

[0116] Comparative Example 5 (Insufficient fibrid treatment, low beating degree)

[0117] A method for preparing aramid insulating paper comprises the following steps:

[0118] (1) The aramid fibrils were processed by pulping machine and deflaking machine, and the specific surface area of ​​the obtained aramid fibrils was 40m 2 / g, beating degree of 52°SR, pulp concentration of 0.16%, and aramid fiber pulp with fiber length greater than 2nm.

[0119] (2) The CTI additives are aluminum oxide and silicon dioxide, with a molar ratio of 15:1 and an addition ratio of 6% of the total dry mass of the fiber. Ultrasonic wet grinding is performed in water to a particle size D90 of 30 μm. Then, acetic acid with a concentration of 0.01 mol / L is carefully added to the additive, and the pH of the solution is adjusted to 3-4. The solution is allowed to stand for 30 minutes, and the pH of the solution is carefully adjusted to neutral with sodium hydroxide solution to form a positively charged colloid.

[0120] (3) 60 parts by weight of the treated aramid fiber slurry, 40 parts by weight of aramid short-cut fibers and the treated CTI additive were mixed and transported to a fourdrinier paper machine through a hydraulic headbox for wet forming. The forming concentration was 0.24% and the ratio of the aramid fiber pulp speed to the forming wire running speed was 0.9.

[0121] (4) The formed paper is pressed and dried to obtain aramid insulation paper base paper containing CTI additives.

[0122] (5) The aramid insulation base paper is hot pressed using an electromagnetic induction high-temperature roller press with a high-temperature roller pressure of 290 N / m and a hot pressing temperature of 295°C to produce 2 mil aramid insulation paper.

[0123] 2. Performance Testing

[0124] The mechanical properties, electrical strength and CTI values ​​of the aramid insulation papers for new energy vehicle drive motors prepared in the examples and comparative examples were tested, and the test results are shown in Table 1 below.

[0125] Table 1: Performance test results of aramid insulation paper prepared in Examples and Comparative Examples

[0126]

[0127]

[0128] As shown in Table 1, the aramid insulation paper for new energy vehicle drive motors prepared in Examples 1-3 has increased additive retention, mechanical properties, electrical strength, and CTI values.

[0129] In Example 4, the CTI additive used only metal oxides without adding silicon dioxide, resulting in insufficient stability of the final colloid, poor effect, reduced additive retention rate, and a decrease in the CTI value.

[0130] The metal oxide used in Example 5 was iron oxide particles. Because the pH of the iron hydroxide colloid is relatively low, it was not adjusted to neutral (otherwise, the colloid would settle, affecting subsequent processing). This resulted in a low retention rate and limited improvement in CTI. Furthermore, iron hydroxide is a yellowish-brown color, resulting in a distinct dark yellow tint in the finished aramid paper, which affects customer use. Other non-ferrous metal oxides, such as copper oxide, also have similar drawbacks.

[0131] In Example 6, the amount of superoxide added to the CTI additive was too much, resulting in poor colloidal stability and poor effect. The retention rate of the additive was reduced, resulting in a decrease in the CTI value.

[0132] Comparative Example 1 is a control group without adding CTI additives. Compared with the data of Example 1, after grinding, activation and positive charge treatment, the use of CTI additives can effectively improve the CTI value of aramid insulation paper, while the mechanical properties and electrical strength of the material are almost unaffected.

[0133] In Comparative Example 2, only silicon dioxide was used as the CTI additive without adding any metal oxide. Due to the chemical stability of silicon dioxide, it was unable to form an electropositive colloid in the subsequent treatment, resulting in a very low retention rate and no effect on improving the CTI.

[0134] In Comparative Example 3, the CTI additive was only ground without activation. Without subsequent activation and positive charge treatment, the retention rate of the CTI additive decreased significantly, and the effect of improving the CTI value of the material was not significant.

[0135] In Comparative Example 4, the surface-activated CTI additive was not adjusted to a neutral colloid state, resulting in insufficient bonding between the additive and the aramid paper. This significantly reduced retention and the CTI value enhancement effect was not significant.

[0136] Comparative Example 5 is a control group with reduced specific surface area and beating degree of aramid fibrids. The fibrids were insufficiently processed and had a low beating degree. The aramid fibrids exhibited a twisted and tangled structure that had not been opened into a film-like structure. This resulted in a significant decline in the overall performance of the aramid insulating paper, a loose and non-dense paper structure, poor uniformity, and decreased electrical strength and CTI values. Despite the addition of a CTI additive, due to the loose structure of the paper caused by insufficient raw material processing, heat from the microstructure of the aramid paper, under the action of voltage and saline solution, was more likely to be locally concentrated on the uneven surface. This resulted in thermal carbonization of the material, the formation of a tracking loop, and even fire. This affected the mechanical properties, electrical strength, and CTI values ​​of the aramid insulating paper, resulting in a decrease in performance.

[0137] It was found in the experiment that the CTI additive particles without surface activation could not form colloids, so no corresponding comparative example was set.

[0138] In the present invention, the electrical strength value and the CTI value are not positively correlated. The essence of CTI is to test the tolerance of the insulating material in an energized salt solution, and whether a conductive path will be formed due to carbonization, and the conductive path will further release heat under the current, catching fire or burning through, causing the insulating material to fail. The principle of the CTI additive is to prevent the carbonization of the conductive path and destroy the carbonized core. For example, polyimide has a very high electrical strength, but a very low CTI value. The electrical strength test itself has some fluctuations. The reason is that the breakdown voltage test itself has fluctuations, so there is a certain detection error. The electrical strength in Comparative Examples 1 and 3 is slightly better than the electrical strength in the embodiment, which is also normal. The technical effect of the present invention mainly reflects the improvement of the CTI value. The retention rate is used to indicate the degree of combination of the additive and the aramid fiber. One of the innovations of the present invention is to introduce a positively charged colloid to combine with the aramid fiber, and to detect the retention rate to indicate this effect.

[0139] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing aramid insulating paper, characterized in that: The following steps are involved: S1. By synergistically controlling the specific surface area, beating degree and fiber length of the aramid fibrids during the pulping and decomposition process, the aramid fibrids were pulped and decompressed and then mixed evenly with aramid short fibers to obtain an aramid fiber slurry; the specific surface area of ​​the aramid fibrids after pulping and decomposition was 70-120 m 2 / g, beating degree is 60-85 o SR, fiber length ≤2 mm; S2. Wet-grinding a CTI additive containing a metal element, then adding a weak acid to adjust the pH, allowing the mixture to stand, and finally adjusting the pH to neutral with an alkaline solution to obtain a treated CTI additive; the CTI additive comprises silicon dioxide and a metal oxide, or the CTI additive comprises silicon dioxide and a metal hydroxide; the molar ratio of silicon dioxide to the metal oxide in the CTI additive is 1:5 to 1:20, or the molar ratio of silicon dioxide to the metal hydroxide in the CTI additive is 1:5 to 1:20; the metal oxide or metal hydroxide is selected from one of magnesium hydroxide, aluminum hydroxide, zinc hydroxide, aluminum oxide, magnesium oxide, or zinc oxide; S3, uniformly mixing the aramid fiber slurry obtained in step S1 and the treated CTI additive obtained in step S2, and wet-forming the mixture, followed by pressing, drying, curling, and high-temperature rolling to obtain aramid insulating paper.

2. The method for preparing aramid insulation paper according to claim 1, characterized in that: In step S2, a weak acid is added to adjust the pH to 3-4.

3. The method for preparing aramid insulation paper according to claim 1, characterized in that: In step S2, the added mass of the CTI additive is 3-7% of the total dry mass of the aramid fibrid and the aramid chopped fibers, and the particle size D90 of the CTI additive after grinding is 5-50 μm.

4. The method for preparing aramid insulation paper according to claim 1, characterized in that: In step S2, the weak acid is selected from one of citric acid and acetic acid, and the concentration of the weak acid is 0.05-0.15 mol / L; the weak acid is added to adjust the pH to 3-4 and the standing time is 20-40 min; the alkali solution is selected from one of a strong base or a weak base, the strong base is sodium hydroxide, and the weak base is ammonia water.

5. The method for preparing aramid insulation paper according to claim 1, characterized in that: The CTI additive is composed of silicon dioxide and aluminum oxide, the molar ratio of silicon dioxide to aluminum oxide is 1:10-15, and the particle size D90 of the CTI additive after grinding is 10-30 microns.

6. The method for preparing aramid insulation paper according to claim 1, characterized in that: In step S2, the CTI of the aramid insulation paper is ≥325V.

7. Use of the aramid insulating paper prepared by the method for preparing aramid insulating paper according to any one of claims 1 to 6 in new energy vehicle motors.

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